If his mother had been encouraged to renounce her citizenship through these atrocious tax laws he might never have returned to the US, even if he retained his citizenship.
Under $90K and you pay taxes on your income in another country, and you didn't earn any of it in the states, you can exempt it entirely. Over $90K, you can take the foreign earned income tax exemption AND then deduct your foreign taxes from the rest using a complicated formula. This year I did all my taxes the long way (deducted my Chinese taxes) as I didn't fit the domicile requirement, but the result was the same.
If you live in a high tax country, you usually do not owe to the states; that wouldn't be fair right?